Creation and update maintenance of maps has traditionally been an expensive and time consuming process. Hand-drawn maps generated from manual survey information are expensive to produce and difficult to maintain and correct. Every feature of the geographic area to be mapped must be surveyed, generating enormous quantities of information. This information is then analyzed, and map drawings corresponding to the survey information are created. Since the survey information is gathered manually, there is ample opportunity for the introduction of errors, such as by erroneous recording of survey information by the surveyors or misinterpretation of survey information by the map drawers. In the event that an error is introduced into a map, that portion of the map containing the error must be manually redrawn, which in itself is a time consuming and expensive process. This is equally true of changes in the geographic area resulting, for example, from changes in street location or direction.
Some of these inefficiencies in the map generation and maintenance process are addressed through the use of a Geographic Information System (GIS) such as ARC/INFO, which is a commonly used geographic information database system, or a Computer Aided Drafting (CAD) system employed for cartography. ARC/INFO provides storage management for both graphical and tabular information. From such a database, maps of geographic areas can be displayed on a computer screen, or can be printed on a computer printer or plotter.
In a Geographic Information System, geographic features such as roads, boundaries, and other spatially dispersed objects are represented within the system as symbolic entities described by one or more sets of coordinates and descriptive information regarding the attributes of the geographic feature represented. These symbolic entities may be generally classified into the following types: point entities, linear entities (including line segments or contiguous groups of line segments referred to in the art as arcs or polylines), area entities (areas bounded by linear entities, referred to in the art as polygons), and annotative entities (text information not attached to a particular spatial entity, although located on the map at a particular spatial coordinate).
The use of ARC/INFO and other GIS or CAD systems has greatly eased the task of maintaining an existing map of a geographic area by automating the process of drawing a map from the survey data. However, use of such a system does not address the inefficiencies involved in obtaining the survey information in the first place. If traditional manual survey techniques are used, the information obtained in the survey must still be manually entered into a computer for inclusion in the GIS database. Besides being tedious, time consuming, and expensive, this process is fraught with the potential for erroneous input of data.
An alternate survey technique involves the use of aerial photography of the geographic area to be mapped, followed by the digitization of the information from the photographs into the database. This process is more efficient than manual survey techniques in that aerial photography gathers information in photographic form quickly, and the digitization process eliminates much of the manual entry of information. However, digitization of aerial photographs still involves the manual effort of tracing the geographic features to be mapped on the photographs, and still requires a substantial expenditure of time and effort. In addition, the aerial method is ill suited to annotation of existing maps with attribute information such as the location of fire hydrants, or street addresses since this information is not readily discernable from an aerial photograph.
A more recent technology capable of increased efficiency over traditional survey techniques involves the use of Global Positioning Satellites (GPS). These satellites can be used with an appropriate GPS receiver to determine the location of the receiver in latitude, longitude, and altitude. By placing such a receiver in a vehicle, a path to be mapped can be driven by the vehicle, with the GPS receiver capturing position information at specified time intervals along the path. In this way, information can be quickly obtained on the location of points along the path, and such information can be used for the generation of maps. Unfortunately, the information obtained from a GPS receiver is not in a form which is usable by a GIS database manager such as ARC/INFO. Prior art system have solved this problem by having the surveyors return to the laboratory or office with the captured GPS data, and executing a computer program which converts the data from the GPS format to a GIS format.
While the above improvements to traditional mapping techniques have significantly increased the efficiency of map creation and maintenance, several inefficient and cumbersome areas remain. For example, existing GPS systems process captured GPS data after returning from the field. If after processing the data into the GIS database it is learned that additional information is needed, a second trip to the field is necessary to gather the missing information. This could occur, for example, during the mapping of city streets if the surveyors fail to travel down all of the streets in the survey area.
In addition, prior art GPS data systems store only location and time information. Mapping involves much more than merely plotting the location of streets or paths. Other geographic features are often equally important, such as street addresses, the locations of fire hydrants or street signs, or any other information which could conceivably be included in a map. There is no facility in existing GPS systems for annotating or updating an existing map database with new attribute information.
Another difficulty with present GPS systems is the lack of a real time operator interface with the system. For example, when mapping a complicated grid of paths such as that formed by city streets, it is necessary to keep track of where the mapping vehicle has been in order to avoid retracing paths and to ensure that no paths are missed. It is difficult and inconvenient to manually keep track of the traced path, and existing GPS data capture systems provide no facility for automatically documenting traced paths and displaying this information to the operator.